Conventionally, a diagnosis to a patient who might have had cerebral infarction, cerebral hemorrhage or the like is performed, using a X-ray computerized tomography system, a MRI (magnetic resonance image) tomography system, a positron emission tomography system utilizing positron emission or the like.
On the other hand, in research on recognition of sound signals, it has come to be known that a speech can be recognized to a considerable extent without hearing a complete sound signal, that is, even if a component of a sound signal is subjected to noise by a certain method. Such a technique is disclosed in, for example, reference 1 (Shannon, R. V., et. al, “Speech Recognition with Primarily Temporal Cues”, SCIENCE, 1995, no. 270, pp. 303 to 305), reference 2 (an article of an auditory sense study group of Acoustical Society of Japan, “Speech perception based on temporal amplitude change with spectrally degraded synthetic sound” by Yoshihisa Obata and Hiroshi Rikimaru, 1999, H-99-6), reference 3 (an article of an auditory sense study group of Acoustical Society of Japan, “Intelligibility of synthesized Japanese speech sound made of band noise—preliminary study for a speech recognition processor utilizing central auditory function—” by Yoshihisa Obata and Hiroshi Rikimaru, 2000, H-2000-3).
According to such references, a sound signal is divided into four frequency bands (0 to 600, 600 to 1500, 1500 to 2500, 2500 to 4000 Hz), each sound signal is subjected to half-wave rectification and is applied to a 16 Hz lowpass filter so as to obtain an amplitude envelope of each frequency band, and is multiplied by a band noise corresponding to each frequency band, and the thus obtained signals are added to generate a signal. Such a signal is referred to as “Noise-Vocoded Speech Sound”. It has been reported that when people with normal hearing ability heard the Noise-Vocoded Speech Sound, an intelligibility of about 80% was obtained.
Conventionally, X-ray computerized tomography systems, MRI (magnetic resonance image) tomography systems, positron emission tomography systems utilizing positron emission and the like have been used to diagnose a disease of a patient who might suffer from a neural disorder stemming from cerebral infarction, cerebral hemorrhage or the like. Although the use of these systems is an effective approach to detect an injured part or a focal part, this approach is an anatomical diagnosis of a disordered site and has a difficulty in diagnosing the function. If there is a simple method for diagnosing the function that cannot be clarified only by anatomical images without using a large scale device, such a method can achieve easy diagnosis. Furthermore, there is also a demand for diagnostic devices for a disorder such as presbycusis, congenital deafness, hearing impairment with independent of the neural disorder.